1. Field of the Invention
This invention generally relates to a method for rapidly and inexpensively determining the presence or absence and level or concentration of microbial contaminants in a liquid sample. More particularly, the invention provides a simplified assay which includes an indicator compound which visibly changes color upon reduction. This assay is particularly useful in detecting microbial contamination in cooling water towers, drinking water, food processing operations, medical laboratories, and other industrial processes.
2. Description of the Prior Art
The contamination of liquid, especially water, with microorganisms can be a major problem in a variety of industrial applications, for example delivery and production of drinking water, food processing operations, medical laboratory processes and industrial cooling towers. The presence of the microorganisms can be dangerous to the health of the population and can also result in damage to industrial processing equipment. Therefore, it is recommended that frequent testing be conducted to detect the presence and/or concentration of microbial contaminants.
The techniques currently in use require approximately 24 to 72 hours to assess the contaminants in the liquid sample. In addition, the results of the testing may be difficult to interpret or quantify. Often, specialized equipment is required to analyze or obtain the results of the testing. Furthermore, the tests are often expensive. As a result of the problems and complications with the current methods of testing, the recommended amount of testing is not completed. Moreover, due to the extensive length of time required to obtain the results, the data will not accurately represent the conditions at the time the test results are determined and often inadequate or improper treatment will occur.
An assay which detects a threshold level of microbial contamination is particularly useful in assessing water in cooling towers. Industrial cooling towers are commonly used to reduce and dissipate heat generated from industrial processes. It is common, especially in warm temperature conditions, for biofilms to form on the pipes from bacteria and the like. The biofilms reduce the heat exchange which occurs between the fluid in the pipes and the cooling tower water. The inadequate cooling by the cooling tower water results in an elevated process liquid temperature which can lead to damage to the process equipment. Therefore, it is necessary to reduce bacterial contamination to a manageable level. However, the addition of excess quantities of biocides or bacterial growth inhibitors is not desirable due to the environmental impact, the high cost of the chemicals and the difficulties in disposing of the water which has been treated. Therefore, it is important to rapidly determine a threshold level of contamination, so that an appropriate treatment course can be followed.
U.S. Pat. 5,206,151 to Robertson describes a technique which requires multiple dilutions and titrations for determining the minimum amount of biocides or antimicrobial agents necessary to control microbial growth. In addition, the Robertson method requires the addition of nutrient matter to accelerate microbial activity in the contaminated sample.